This invention relates to computer printers and scanners and, more particularly, to vibration suppression in computer printers and scanners.
Vibration suppression technology developed by the inventor herein has been described in his U.S. Pat. Nos. 4,916,635 and 5,638,267 and in pending patent application Ser. No. 09/262,781 filed Mar. 4, 1999. The teachings of these patents and patent application are incorporated herein by reference. The technology disclosed in these references is referred to by the registered trademark Input Shaping®. As disclosed in these references, commands to a physical system are processed based on knowledge of system parameters such as vibrational frequencies, damping ratios, or measured system response, and system limitations. In particular, with knowledge of natural frequency and damping ratio, a desired input command is “shaped” so that the physical system is moved from an initial state to a final state with eliminated or suppressed residual vibration.
The elimination or suppression of residual vibration reduces settle times for machinery and/or reduces excessive acoustic noise that would occur without the use of the anti-vibration technology. The use of knowledge of vibrational frequencies and a damping estimate to generate new commands provides the unusual benefits set forth in the patents and patent application mentioned above. Techniques prior to the teachings in the patents set out above did not use such knowledge or if they did, the techniques were computationally expensive or impractical. As a result, commercial printer products and similar scanning devices do not use knowledge of vibrations or system response, and system limitations as part of their command generation process. Furthermore, the techniques set forth in the patents and patent application mentioned above can “target” specific frequencies thus yielding particularly good trajectories that are fast and vibration reducing. Other approaches tend to smooth trajectories in an effort to reduce vibrations or acoustics and therefore incur large time penalties. The techniques set forth in the patents and patent application mentioned above are therefore not just smooth versions of an unshaped command and are designed to match a particular system.
Computer printers create images by moving a print head (often called an ink pen) across the paper. As demand for high-speed printing increases, the speed of the print head translation increases, the speed of the paper advance increases, and the speed of the print head dot generation (e.g. ink jet frequency) increases. Current printers move fast enough that they start to excite vibrations. First, vibrations within the printer require that the printer pause between each scan across the paper or alternatively require that the width of the printer be increased to accommodate the over travel needed to accelerate and decelerate the print head without vibrations. Second, accelerations induced by the scanning motion of the print head excite vibrations of the entire printer and the table on which it is placed. Third, fluid dynamic vibrations interact with the dot generation process for ink jet printing. Further, fluid dynamic interactions among ink channels interact with the ink jet dot generation process. Fluid dynamic vibration reduction can be used to increase dot generation speed and to improve the quality and repeatability of dot generation and reduce spatter. Lastly, advancement of the paper between scans of the print (or scan) head can excite vibrations of the printer, table, and the paper itself.
With the newest generation of printers, the accelerations are high enough to annoy many computer users. The printer shakes the table so that no other equipment can be used at the same time. For example, if a monitor resides on the same table, it may become difficult to read because the table is shaking. The same holds true for computer scanners. The scanning element is moved across the paper, or a negative or photograph is moved across the element. As the scan speed increases, vibrations and their undesirable effects increase. Thus there is a need for vibration control technology to be applied to the current generation of high speed printers and scanners.